1. Comments on the gas system Issues of scale What gas mix? Summary Karol Lang The University of Texas at Austin NuMI Off-axis Experiment Detector Workshop SLAC, Jan 24-26, 2003

2. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 2 The Scale – crude assumptions 20 x 20 m 2 2 mm gap 0.8 m 3 ~ 1 m 3 / plane 500-plane detector 500m 3 total 200,000 m 2 (40 acres) ( 1A-type cylinder of Ar contains ~8 m 3 of gas) Need ~60 gas cylinders to fill the detector 2 x 2 m 2 chambers 100 chambers / plane 50,000 chambers 1 cm Aq overpressure F = 400 N >> 50,000 Swagelock (?) fittings ($1.8 / piece in brass) For LSTs it would be 5-10 (?) times larger volume

3. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 3 Main issues for a large gas system Safety Gas mixing and supply Gas distribution and flow control Hermeticity and purity of the system Gas circulation and purification (or exhaust) Gas system monitoring Long term reliability Assure all (or most ?) of the above inexpensively !!

4. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 4 Large gas system of the past MACRO ~ 500 m 3 1 volume exchange in 5 days He – n-pentane mix Soudan-2 ~600 m 3 Ar-CO2 ~8.5 m 3 / week leak $30-40k / year

5. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 5 Safety Safety of personnel – »non-flammable »non-toxic »standard (easy) handling Safety of the detector »chemically non-aggressive mix »benign radicals (plasma chemistry!) »avoid mechanical (pressure) stresses Safety of the environment »environmentally friendly

6. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 6 Precision of the mix Ambient T, p, humidity factors Automatic control and monitoring of the mix Cylinder exchange Gas mixing and supply Balance flow to all chambers Flow monitoring (electronic and/or visual) Overpressure protection Modularity (chamber/units replacement ?) Computerized gas flow control What flow rate ? Purging (high rate?) flow Gas distribution and flow control

7. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 7 Gas distribution – e.g., Belle Functional schematics from Belle (courtesy of D. Marlow) Important! (also implemented in Soudan-2)

8. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 8 Avoid porous components –avoid O 2 –avoid H 2 0 –perhaps other constraints Sieves, scrubbing Test points for monitors Offline performance: chromatography / mass spectroscopy Online performance – radioactive sources / CR ( monitoring) Hermeticity and gas purity Gas recirculation and purification (or exhaust) Cannot afford not to circulate ?! Cost of operation with exhaust Cost of recirculating system and its maintenance What flow rates ? Variable flow rates ? How non-hermetic (contaminated system) Watch back pressure (w/ redundancy)

9. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 9 Gas exhaust example - Belle (courtesy of D. Marlow)

10. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 10 Monitor everything gas mixing gas flow bubblers actual gas mix circulation chamber performance chamber currents Gas system monitoring and control Constant gas mix Robust monitoring / controlling Cylinder exchange Replacements of sieves and manifolds Purification Circulation Long term reliability

11. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 11 What gas mix? – personal view RPC gas mix: –Quenching of the streamer / avalanche Electron-ion pairse.g., Ar Electron quenchinge.g., SF6, HFC-134a, HFC-13B1 Photon quenchinge.g., iC 4 H 10 –Signal size ~10-1000 pC RPC gas problems: Aggressive radicals: HF x Water Plasma chemistry Not enough known! Monte carlo programs: Magboltz, Imonte, Heed,.. - how helpful? Conclusions: –avoid HF –Freonless mixes

12. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 12 RPC gas mix examples BaBar RPCs Ar – iC 4 H 10 -Freon 13B1 (TDR) 59% - 37% - 4% Study of non-flammable, freonless mixes Belle RPCs Ar – iC 4 H 10 - HFC 134A 30% - 8% - 62% Study of non-flammable, freonless mixes ARGO-YBJ Ar – iC 4 H 10 -C 2 H 2 F 4 45% - 45% - 10% 60% - 27% - 13% 75% - 15% - 10% Study of non-flammable, freonless mixes

13. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 13 Belle studies – freonless mix

14. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 14 Belle studies

15. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 15 Belle Freon ADC TDC

16. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 16 ARGO-YBJ

17. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 17 Summary Large volume gas systems (i.e., similar to off-axis detector) have been operated in the past ! For a large off-axis RPC system more touchy issues revolve around uniform distribution of flow avoidance of over-pressure remote control and monitoring (of everything) Likely need of circulation/purification system Need some R&D: Find acceptable safe freonless mix. Study signals (size, after-pulsing, x-talk…) readout. How dirty can the gas be (contamination, purification)? What is the minimal flow rate?

18. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 18

19. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 19 Another gas system example – BaBar DCH

20. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 20

21. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 21

22. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 22

23. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 23 ARGO-YBJ

24. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 24 ARGO-YBJ

25. Karol Lang, NuMI Off-axis Experiment Detector Workshop, SLAC, Jan 24-26, 2003 25